Disorders of calcium, phosphate and magnesium. Flashcards Preview

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Flashcards in Disorders of calcium, phosphate and magnesium. Deck (49):
1

What is the physiological importance of calcium?

- Muscle contraction
- Neuronal excitation
- Enzyme activity (Na/K ATPase, hexokinase etc.)
- Blood clotting

2

What is the structural importance of calcium?

Key component of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ - the predominant mineral in bone

3

What is the physiological importance of phosphate (PO4-)

- The P in ATP – our fuel!
- Intracellular signalling
- Cellular metabolic processes e.g. glycolysis

4

What is the structural importance of phosphate?

- Backbone of DNA
- Component of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂
- Membrane phospholipids

5

What is the physiological importance of magnesium?

- Cofactor for ATP
- Neuromuscular excitability
- Enzymatic function
- Regulates ion channels

6

What is the normal range for calcium?

2.20 -2.60 mmol/L

7

What are the two key controlling factors for calcium?

- PTH
- Vitamin D and metabolites

8

What processes is calcium related to/involved in?

- GI uptake
- Renal Clearance
- Bone

9

What is plasma calcium?

Total Ca = Ionised Ca + Bound Ca + Complexed Ca

10

What is ionised calcium?

Physiologically active fraction
- Calcium sensing receptor
- Cellular Effects
- Regulation of PTH

11

What is bound calcium?

Bound Calcium
- Physiologically inactive
- Albumin main binding protein (~50%)

12

What is complexed calcium?

Salts – calcium phosphate & calcium citrate

13

What can calcium values be corrected for?

Changes in albumin. Better diagnostic performance.

14

What effect does acidosis have on Ca-albumin?

Reduces Ca-albumin

15

What effect does alkalosis have on Ca-albumin?

Increases Ca-albumin

16

What can alkalosis precipitate?

Tetany

17

What are the endogenous factors related to Vit D absorption?

- Skin colour
- Aging

18

What are the exogenous factors related to Vit D absorption?

- Ozone
- Sunscreens & clothing
- Latitude and season
- Time of day
- Diet & supplements

19

What factors cause vitamin D to fail?

- Age
- Body fat
- BMI

20

What is the role of parathyroid hormone (PTH)?

Acts on bone, GI and kidney to increase levels of ionic calcium. Increased ionic Ca acts upon the parathyroid glands to stop the release of PTH.

21

What is the effect of PTH on the kidney?

Decreases Ca clearance but increases phosphate excretion.

22

What is the effect of PTH on bone?

Increases Ca turnover with net resorption.

23

What is the effect of PTH on the gut?

Stimulates the kidney to release vit D.
Vit D increases Ca absorption from the gut.

24

What are the causes of hypocalcaemia?

- Hypoproteinaemia
- Vit D deficiency
- Hypoparathyroidism
- Inadequate intake of Ca
- Pseudohypoparathyroidism
- Artefactual causes

25

What are the causes of Vit D deficiency?

- Dietary / Malabsorption
- Hepatic disease
- Renal Disease
- End organ Vitamin D resistance

26

What are the causes of hypoparathyroidism?

- Primary
- Secondary to Mg depletion

27

What is the cause of pseudohyoparathyroidism?

End organ PTH resistance.

28

What are the artefactual causes of hypocalcaemia?

- EDTA contamination
- Venestasis will cause low adjusted calcium (total calcium is unaffected)

29

How can you tell the difference between hypoparathyroidism and Vit D deficiency?

Vit D deficiency - High PTH, low Ca

Hypoparathyroidism - rock bottom PTH, low Ca

30

What are the possible causes of hypercalcaemia?

Hyperparathyroidism

Malignancy
- Lytic lesions
- Humoral eg PTHrp

Drugs

Vitamin D excess
- 1a cholecalciferol
- Sarcoidosis

Bone disease + immobilisation

31

What is the most common cause of ludicrously serum high potassium.

EDTA comtamination

32

What are the differential diagnoses of hypercalcaemia?

- Consider Adjusted Ca: look at the albumin
- Check drug history
- Exclude excess vitamin D intake
- Check for renal failure
- Simultaneous measurement of Ca & PTH
- Consider rarer causes & more complex investigations

33

How can you tell the difference between hyperparathyroidism and bone metastases?

Hyperparathyroidism - high PTH, high calcium

Metastases - low PTH, high calcium

34

What are the causes of phosphate deficiency?

Hyperparathyroidism

Excess losses
- renal tubular damage
- Gastro intestinal
- diabetes (diuresis)

Poor intake
- malnutrition
- inadequate IVN

ECF / ICF redistribution - like potassium

35

What are the signs/symptoms of phosphate deficiency?

- Haemolysis, thrombocytopenia and poor granulocyte function
- Severe muscle weakness, respiratory muscle failure and rhabdomyolysis
- Confusion, irritability and coma may be due to a metabolic encephalopathy due to phosphate deficiency
- Renal dysfunction

36

What is hypomagnesaemia associated with?

Hypokalaemia Hyponatraemia Hypophosataemia
Hypocalcaemia

37

What are the renal causes of magnesium depletion?

- Diuretic phase of Acute
- Tubular Necrosis
- Hypercalcaemic states
- Drugs
-- Antibiotics - gentamicin/carbenicillin
-- Chemotherapy - cisplatin
-- Diuretics
-- FK506

38

What are the GI causes of magnesium depletion?

- Malnutrition
- Intravenous nutrition
- Diarrhoea
- Malabsorption

39

What are the cellular effects of magnesium depletion?

- Reduced mitochondrial respiration & impaired phosphorylation
- Defective Na-K ATPase activity
- Impaired DNA synthesis

40

What are the biochemical effects of magnesium depletion?

- Hypocalcaemia
- Hypophosphataemia
- Hypokalaemia

41

What are the endocrine effects of magnesium depletion?

- Impaired PTH release
- PTH resistance in bone

42

What are the cardiovascular effects of magnesium depletion?

- Cardiac irritability
- Reduced contractility

43

What are the CNS effects of magnesium depletion?

- Hyper-reflexia
- Tetany
- Ataxia / Vertigo
- Psychosis / Depression

44

What are the muscle effects of magnesium depletion.

- Weakness
- Muscle fibrillation
- Myopathic EMG

45

What is the relevance of serum magnesium?

- Poor correlation with Mg status
- Of value acutely

46

What is the relevance of erythrocyte Mg?

- Poor correlation with Mg status
- Affected by high reticulocyte count

47

What is the relevance of leukocyte Mg?

- Good correlation
- Good predictive value

48

What is the relevance of muscle Mg?

- 20% body mass
- important physiologically
- requires biopsy

49

When should magnesium screening be considered?

With combined hypokalaemia and hypocalcaemia

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